1. Cell cycle and Cell division ACh
Bio 103
Cell cycle and Cell division
ACh

2. Overview: The Key Roles of Cell Division
The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter
The continuity of life is based on the reproduction of cells, or cell division
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3. 6.1 Overview of cell division
Functions of cell division
In unicellular organisms, division of one cell reproduces the entire organism
Multicellular organisms depend on cell division for
Development from a fertilized cell
Growth
Repair
Production of gametes
Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division
Growth: You started out as a single cell after mom’s egg met dad’s sperm, but today you have about 10 trillion cells in your body. All of those cells were produced from that first cell and its descendents by mitosis. When you watch plants grow taller or baby animals grow into adults, you’re seeing mitosis at work.
Repair: It’s a fact of life that cells wear out and need to be replaced. For instance, you constantly shed skin cells from your surface. If your body couldn’t replace these cells, you’d run out of skin. And if an organism gets injured, its body uses mitosis to produce the cells necessary to repair the injury.
Production of gametes: During sexual reproduction, gametes (cells, specifically eggs and sperm, containing half the genetic information of their parent cells) get together to make new individuals. When the genetic information of the gametes joins together, the new individual has the correct total amount of DNA.
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4. (b) Growth and development
Figure 12.2
100 m
(a) Reproduction
200 m
(b) Growth and development
Figure 12.2 The functions of cell division.
20 m
(c) Tissue renewal

5. 6.1 Overview of Cell Division
Concept: Most cell division results in genetically identical daughter cells
Most cell division results in daughter cells with identical genetic information, DNA
The exception is meiosis, a special type of division that does not produce identical genetic information - can produce sperm and egg cells
© 2011 Pearson Education, Inc.

6. 6.2 Cell division in Prokaryote
Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission
Single chromosome makes a copy of itself
The plasma membrane pinches inward, dividing the cell into two

7. Chromosome replication begins. Two copies of origin
Figure
Cell wall
Plasma membrane
E. coli cell
Bacterial chromosome 1
Chromosome replication begins.
Two copies of origin
Figure Bacterial cell division by binary fission.

8. Chromosome replication begins. Two copies of origin
Figure
Cell wall
Plasma membrane
E. coli cell
Bacterial chromosome 1
Chromosome replication begins.
Two copies of origin 2
Replication continues.
Figure Bacterial cell division by binary fission.

9. Chromosome replication begins. Two copies of origin
Figure
Origin of replication
Cell wall
Plasma membrane
E. coli cell
Bacterial chromosome 1
Chromosome replication begins.
Two copies of origin 2
Replication continues. 3
Replication finishes.
Figure Bacterial cell division by binary fission.

10. Chromosome replication begins. Two copies of origin
Figure
Origin of replication
Cell wall
Plasma membrane
E. coli cell
Bacterial chromosome 1
Chromosome replication begins.
Two copies of origin 2
Replication continues. 3
Replication finishes.
Figure Bacterial cell division by binary fission. 4
Two daughter cells result.

11. 6.3 Cell division in eukaryotes
Cellular Organization of the Genetic Material
All the DNA in a cell constitutes the cell’s genome
A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells)
In eukaryotes, DNA is complexed with proteins called histones to form chromatin
Chromatin in a cell are packaged into chromosomes
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12. 6.3 Cell division in eukaryotes
Cellular Organization of the Genetic Material
Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
Number of chromosomes in a human (male)
© 2011 Pearson Education, Inc.

13. Karyotype
A picture of the chromosomes from a human cell arranged in pairs by size
First 22 pairs are called autosomes
Last pair are the sex chromosomes
XX female or XY male

14. 6.3 Cell division in eukaryotes
Cellular Organization of the Genetic Material
Somatic cells (non reproductive cells) have two sets of chromosomes
Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells

15. 6.3 Cell division in eukaryotes
Cellular Organization of the Genetic Material
In preparation for cell division, DNA is replicated and the chromosomes condense
Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), which separate during cell division
The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached
© 2011 Pearson Education, Inc.

16. The process of cell division
6.3 Cell division in eukaryotes
The process of cell division
During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei
Once separate, the chromatids are called chromosomes
© 2011 Pearson Education, Inc.

17. Chromosomal DNA molecules
Figure
Chromosomal DNA molecules
Chromosomes 1
Centromere
Chromosome arm
Figure 12.5 Chromosome duplication and distribution during cell division.

18. Chromosomal DNA molecules
Figure
Chromosomal DNA molecules
Chromosomes 1
Centromere
Chromosome arm
Chromosome duplication (including DNA replication) and condensation 2
Sister chromatids
Figure 12.5 Chromosome duplication and distribution during cell division.

19. Chromosomal DNA molecules
Figure
Chromosomal DNA molecules
Chromosomes 1
Centromere
Chromosome arm
Chromosome duplication (including DNA replication) and condensation 2
Sister chromatids
Figure 12.5 Chromosome duplication and distribution during cell division.
Separation of sister chromatids into two chromosomes 3

20. Phases of the Cell Cycle
Eukaryotic cell division consists of
Interphase, cell growth and copying of chromosomes in preparation for cell division
Mitosis, the division of the genetic material in the nucleus
Cytokinesis, the division of the cytoplasm
Gametes are produced by a variation of cell division called meiosis
Meiosis yields non identical daughter cells that have only one set of chromosomes, half as many as the parent cell
© 2011 Pearson Education, Inc.

21. Phases of the Cell Cycle
G1 - primary growth phase, cell grows larger
S – synthesis; DNA replicated
G2 - secondary growth phase, DNA is checked by enzymes for mistakes and repaired
M - mitosis
C - cytokinesis
Interphase ~ 90% of the time.

23. Mitosis is conventionally divided into four phases
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis overlaps the latter stages of mitosis
For the Cell Biology Video Myosin and Cytokinesis, go to Animation and Video Files.
© 2011 Pearson Education, Inc.

24. Prophase Chromatin condenses (coils) into chromosomes.
Sister chromatids joined by centromere.
Nuclear membrane dissolves.
Centrioles divide and move to opposite poles forming spindle between them.
Prophase
Prophase occupies over half of mitosis. The nuclear membrane breaks down. A structure known as the centrosome duplicates itself to form two daughter centrosomes that migrate to opposite ends of the cell. The chromosomes condense into compact structures. Each replicated chromosome can now be seen to consist of two identical chromatids (or sister chromatids) held together by a structure known as the centromere.

25. Metaphase… Sister chromatids line up on metaphase plate.
Centromeres lock on to spindle fibre
Metaphase
The chromosomes align themselves along the metaphase plate of the spindle apparatus.

26. Anaphase Centromeres divide.
Spindle fibers contract pulling sister chromatids apart to poles
Anaphase
The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by spindle fibres. The separated sister chromatids are now referred to as daughter chromosomes.

27. Telophase New nuclear membranes form around new nuclei Telophase
The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the chromosomes uncoil and become diffuse, and the spindle fibres disappear.

28. Chromosome, consisting of two sister chromatids
Figure 12.7
10 m
G2 of Interphase
Prophase
Prometaphase
Metaphase
Anaphase
Telophase and Cytokinesis
Centrosomes (with centriole pairs)
Chromatin (duplicated)
Early mitotic spindle
Fragments of nuclear envelope
Nonkinetochore microtubules
Aster
Metaphase plate
Cleavage furrow
Nucleolus forming
Centromere
Figure 12.7 Exploring: Mitosis in an Animal Cell
Plasma membrane
Nucleolus
Nuclear envelope
Chromosome, consisting of two sister chromatids
Kinetochore
Kinetochore microtubule
Nuclear envelope forming
Spindle
Centrosome at one spindle pole
Daughter chromosomes

29. Cytokinesis
In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow
© 2011 Pearson Education, Inc.

30. Cell now returns to interphase
The chromosomes uncoil back into chromatin
The whole cell cycle starts over again

31. Figure 12.UN06
Figure 12.UN06 Appendix A: answer to Test Your Understanding, question 10

32. Name the Mitotic Stages:
Interphase
Prophase
Telophase
Metaphase
Anaphase

33. Mitosis Animation

34. Locate the Four Mitotic Stages in Plants
Anaphase
Telophase
Metaphase
Prophase

35. Uncontrolled Mitosis Cancer cells
If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors
Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell
Cancer cells

36. Meiosis
Another type of cell division that halves the number of chromosomes
Meiosis yields non identical daughter cells that have only one set of chromosomes, half as many as the parent cell
Produces gametes (eggs & sperm)
Occurs in the testes in males
Occurs in the ovaries in females

37. Meiosis
Figure 13.7
Interphase
Homologous pair
of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes 1 2
Homologous
separate
Haploid cells with
replicated chromosomes
Sister chromatids
Haploid cells with unreplicated chromosomes
Meiosis I
Meiosis II
Meiosis reduces the number of chromosome sets from diploid to haploid
Meiosis takes place in two sets of divisions
Meiosis I reduces the number of chromosomes from diploid to haploid
Meiosis II produces four haploid daughter cells

38. Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment

39. Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half
Fertilization then restores the original number of chromosomes
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right number!

40. A Comparison Of Mitosis And Meiosis
Prophase
Duplicated chromosome
(two sister chromatids)
Chromosome
replication
Parent cell
(before chromosome replication)
Chiasma (site of
crossing over)
MEIOSIS I
Prophase I
Tetrad formed by
synapsis of homologous
chromosomes
Metaphase
Chromosomes
positioned at the
metaphase plate
Tetrads
Metaphase I
Anaphase I
Telophase I
Haploid
n = 3
MEIOSIS II
Daughter
cells of
meiosis I
Homologues
separate
during
anaphase I;
sister
chromatids
remain together
Daughter cells of meiosis II n
Sister chromatids separate during anaphase II
Anaphase
Telophase
Sister chromatids
separate during
anaphase 2n
Daughter cells
of mitosis
2n = 6

41. Difference between mitosis and meiosis
Number of divisions 1 2
Number of daughter cells 4
Genetically Identical
Yes No
Number of chromosomes
Same as parent
Half of parent
Where in the body
Somatic cells
Gametes
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction

42. MUTATIONS
Changes in DNA that affect genetic information

45. A mutation is a change in the sequence of nucleotides in DNA
Mistakes Happen: The Consequences of Mutation
A mutation is a change in the sequence of nucleotides in DNA
Mutations in DNA lead to changes in RNA, which can lead to changes in proteins.
When proteins change, the functions of cells and the traits of organisms can also change.

46. Gene Mutations Point Mutations – changes in one or a few nucleotides
Substitution
THE FAT CAT ATE THE RAT
THE FAT HAT ATE THE RAT
Insertion
THE FAT CAT XLW ATE THE RAT
Deletion
THE FAT ATE THE RAT

47. Gene Mutations
Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function.
Insertion
THE FAT CAT ATE THE RAT
THE FAT HCA TAT ETH ERA T
Deletion
TEF ATC ATA TET GER AT H H

48. Significance of Mutations
Most are neutral
Eye color
Birth marks
Some are harmful
Sickle Cell Anemia
Down Syndrome
Some are beneficial
Sickle Cell Anemia to Malaria
Immunity to HIV

49. What Causes Mutations? Parent to child Environmental damage
There are two ways in which DNA can become mutated:
Mutations can be inherited.
Parent to child
Mutations can be acquired.
Environmental damage
Mistakes when DNA is copied

50. Chromosome Mutations Down Syndrome
Chromosome 21 does not separate correctly.
They have 47 chromosomes in stead of 46.
Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence.

51. Sex Chromosome Abnormalities
Klinefelter’s Syndrome
XXY, XXYY, XXXY
Male
Sterility
Small testicles
Breast enlargement

52. Sex Chromosome Abnormalities
XYY Syndrome
Normal male traits
Often tall and thin
Associated with antisocial and behavioral problems

53. Sex Chromosome Mutations
Turner’s Syndrome X
Female
sex organs don't mature at adolescence
sterility
short stature

54. Sex Chromosome Mutations
XXX
Trisomy X
Female
Little or no visible differences
tall stature
learning disabilities
limited fertility

56. Now find out how some of them were mutated?